Other Comprehensive Income (Schedule of Changes in AOCL by Component) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	$ (5,100,000)	$ (66,900,000)	$ 4,900,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	2,200,000	4,200,000	2,000,000.0
Other Comprehensive Income (Loss), before Tax, Total	(7,300,000)	(71,100,000)	2,900,000
Other Comprehensive Income (Loss), Tax	9,600,000	7,000,000.0	(5,900,000)
Other comprehensive income (loss)	2,300,000	(64,100,000)	(3,000,000.0)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	7,500,000
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,573,300,000
Other comprehensive income (loss)	2,300,000	(64,100,000)	(3,000,000.0)
Ending balance3	1,726,100,000	$ 1,573,300,000
Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted		—
Derivative Instruments and Hedges [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Tax, Total	(47,500,000)	$ (13,600,000)	16,000,000.0
Other Comprehensive Income (Loss), Tax	11,000,000.0	3,200,000	(3,500,000)
Other comprehensive income (loss)	(36,500,000)	(10,400,000)	12,500,000
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	7,200,000	16,800,000	4,300,000
Other comprehensive income (loss)	(36,500,000)	(10,400,000)	12,500,000
Ending balance3	(29,300,000)	$ 7,200,000	16,800,000
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted		0.8
Derivative Instruments and Hedges [Member] | Foreign Exchange Forward [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Tax, Total	(700,000)	$ 0	700,000
Other Comprehensive Income (Loss), Tax	200,000	0	(100,000)
Other comprehensive income (loss)	(500,000)	0	600,000
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	200,000	200,000	(400,000)
Other comprehensive income (loss)	(500,000)	0	600,000
Ending balance3	(300,000)	200,000	200,000
Derivative Instruments and Hedges [Member] | Interest Rate Swap [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Tax, Total	(39,600,000)	(31,600,000)	17,500,000
Other Comprehensive Income (Loss), Tax	9,100,000	7,300,000	(3,900,000)
Other comprehensive income (loss)	(30,500,000)	(24,300,000)	13,600,000
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,200,000)	18,300,000	4,700,000
Other comprehensive income (loss)	(30,500,000)	(24,300,000)	13,600,000
Ending balance3	(35,700,000)	$ (5,200,000)	18,300,000
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted		0.8
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	34,700,000	$ (40,100,000)	(24,000,000.0)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0
Other Comprehensive Income (Loss), before Tax, Total	34,700,000	(40,100,000)	(24,000,000.0)
Other Comprehensive Income (Loss), Tax	0	0	0
Other comprehensive income (loss)	34,700,000	(40,100,000)	(24,000,000.0)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(145,400,000)	(105,300,000)	(81,300,000)
Other comprehensive income (loss)	34,700,000	(40,100,000)	(24,000,000.0)
Ending balance3	(110,700,000)	(145,400,000)	(105,300,000)
Change in Pension and Postretiremen Defined Benefit Plans [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	900,000	(19,400,000)	7,900,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	4,600,000	2,000,000.0	3,000,000.0
Other Comprehensive Income (Loss), before Tax, Total	5,500,000	(17,400,000)	10,900,000
Other Comprehensive Income (Loss), Tax	(1,400,000)	3,800,000	(2,400,000)
Other comprehensive income (loss)	4,100,000	(13,600,000)	8,500,000
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(44,300,000)	(24,500,000)	(33,000,000.0)
Other comprehensive income (loss)	4,100,000	(13,600,000)	8,500,000
Ending balance3	(40,200,000)	$ (44,300,000)	(24,500,000)
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted		(6.2)
AOCI Attributable to Parent [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other comprehensive income (loss)		$ (64,100,000)	(3,000,000.0)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(182,500,000)	(113,000,000.0)	(110,000,000.0)
Other comprehensive income (loss)		(64,100,000)	(3,000,000.0)
Ending balance3	(180,200,000)	$ (182,500,000)	(113,000,000.0)
New Accounting Pronouncement or Change in Accounting Principle, Description of Prior-period Information Retrospectively Adjusted		(5.4)
AOCI Attributable to Parent [Member] | Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,400,000)
Ending balance3		$ (5,400,000)
Retained Earnings [Member] | Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	5,400,000
Ending balance3		5,400,000
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		5,400,000
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(40,700,000)	(7,400,000)	21,000,000.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(6,800,000)	(6,200,000)	(5,000,000.0)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Interest Rate Swap [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(35,400,000)	(24,800,000)	22,800,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(4,200,000)	(6,800,000)	(5,300,000)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Foreign Exchange
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	1,900,000	(600,000)	400,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(2,600,000)	600,000	300,000
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(7,200,000)	18,000,000.0	(2,200,000)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0
Other Comprehensive Income (Loss), before Tax, Total	(7,200,000)	18,000,000.0	(2,200,000)
Other Comprehensive Income (Loss), Tax	1,700,000	(4,100,000)	500,000
Other comprehensive income (loss)	(5,500,000)	13,900,000	(1,700,000)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	12,200,000	(1,700,000)	0
Other comprehensive income (loss)	(5,500,000)	13,900,000	(1,700,000)
Ending balance3	$ 6,700,000	$ 12,200,000	$ (1,700,000)